As is known, coke ovens may be equipped with one or two offtakes to carry away the volatile products liberated in the coking process. The volatile products pass through a duct in the oven top and enter a refractory lined standpipe, usually called an "ascension pipe," which is connected through a supply pipe to a gas-collecting main. Steam and water are injected into the supply pipe to clean the issuing gases prior to the time that they enter the gas-collecting main. A liquid-sealed valve is provided in the supply pipe, the liquid therefor being derived from the water and steam sprayed onto the issuing gases. At the junction of the top of the ascension pipe and the downwardly-extending supply pipe is a cap valve or "elbow cover" which, when open, vents the oven to the atmosphere. The cover is removed from the ascension pipe while the oven is charged and during the coke pushing operation of the battery.
Prior art elbow covers of this type normally could be opened to permit a cleaning device to be inserted through the opening in the ascension pipe to clean the supply pipe; however, since the opening in the ascension pipe was normally circular in configuration, difficulties were sometimes encountered in manipulating the cleaning device. Furthermore, in prior art elbow covers, tar deposits collect on the inner surface of the cover which burn when the cover is opened, causing pollution of the atmosphere.